If 64-bit was an easy option for you, the transition wasn't after the /3GB switch, it typically happened at about 1GB RAM and yeah, it wasn't very long as you imagined because of Moore's law.

So that /3GB switch is for people who are stuck on the wrong hardware for a variety of reasons, and the timing is about how long those people stayed trapped rather than how long before this became a bad idea (it was a bad idea before it even shipped, but it was necessary)

Linux had some more extreme splits including a 3.5:0.5 split and a nasty 4:4 split (in which all the userspace addresses are invalidated when in kernel space, ugh) and it's for the same reason, these aren't customers who chose not to go to 64-bit, they're customers who can't yet and will pay $$$$ to keep what they are doing working for just a while longer anyway despite that.